A well-known form of harvesting machine is a rotary combine. A typical combine includes a crop harvesting apparatus which reaps grain stalks and feeds the grain stalks to a separating or threshing apparatus. The grain stalks or other crop materials harvested in the field are moved rearwardly from a crop harvesting header assembly and introduced for threshing to the rotor assembly by a crop feeder assembly.
In a rotary combine, the rotor assembly includes a generally tubular rotor housing mounted in the combine body. A driven rotor is coaxially mounted within the housing. The rotor comprises an infeed section and a cylindrical threshing section, and is supported at opposite ends by front and rear bearing assemblies.
The cylindrical threshing section of the rotor and the rotor housing mount cooperating threshing elements which separate grain from other material in a threshing zone. The crop material is threshed as it spirals around the rotor threshing section and passes through openings in the rotor housing.
As discussed in Tanis U.S. Pat. No. 5,387,153, assigned to the same assignee as the present invention, the ability to transfer crop materials from the feeder assembly to the threshing zone of the rotor assembly is a key to efficient combine operations. Most rotary combine rotors include an infeed section impeller comprised of a series of impeller blades arranged at a forward end of the rotor. The impeller blades rotate within a shroud which is a part of the rotor housing. During harvesting operations, the generally linear movement of the crop materials received from the feeder assembly is converted by the rotating impeller blades into a rotating, circulatory movement, in a rearward and outward direction.
When rotary combines are used on certain long-stemmed leguminous or grassy crops, such as windrowed perennial or annual rye grass, clover, and bent grass, there is a potential for portions of such grassy crops to extend into the impeller blades while other portions remain partially engaged with the feeder assembly. The latter portions tend to move toward the axis of rotation of the rotor assembly, and may wrap about the front rotor bearing.
Long-stemmed leguminous or grassy crops also have a tendency to wrap around or "hairpin" about the leading edge of the impeller blades. This hairpinning action can create a buildup of crop materials on the aforementioned leading edge, which reduces the effectiveness of the impeller and further reduces combine efficiency.
Numerous impeller designs, including that disclosed in the Tanis patent, have been proposed to prevent crop materials from becoming entangled with the front rotor bearing and prevent hairpinning about the impeller blades' leading edges. None has been thoroughly successful in doing so, however. Furthermore, these designs suffer from the complexity associated with assembly from a multitude of individual parts, and the higher costs associated therewith.